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Composites
Basics of Composites: A composite is a material made of multiple materials but the most common composites used in 416 are Fiberglass and Carbon Fiber with resin. Prepreg: Prepreg is short for pre-impregnated and refers to a composite material that is sold with the resin already applied. Since resin cures at room temperature the prepreg must be stored in a freezer (ideally at -18 C or 0 to 5 C if freezers are not available) to maintain its use. Making a composite plate or sheet: One very good method for making a fiberglass or carbon fiber sheet is to use a mirror to layup on. First step to do this is to clean the mirror. Windex can be used for this and it generally takes several coats of windex and wiping the get the mirror perfectly clean. After the mirror is clean, you want to put a boarder of masking tape around the area you want to infuse. This will keep the boarder clean so that you can have a good surface to bond the vacuume bag seal. After the boarder is taped, you must apply a coat of Release agent. Our team found that TR-960 multi pull release system worked well. To apply this you must first dampen a cloth with the release agent. Then you will wipe it all over the mirror and allow to dry for a few minutes. Then you will take a clean cloth and wipe all of the excess release agent that you can get off. You will have to repeat the application and wipe-down between 2-4 times or until masking tape will not stick to the mirror surface. The next step is to layup your fiber cloth and core material how ever you desire. You will then have to add a layer of peel ply followed by a layer of mesh. Then once your fibers and peel ply and mesh are placed how you want them you will have to pull up the masking tape boarder and attach the vacuum bag. When attaching the vacuum bag make sure to use plenty of pletes and extra bag. Then you can infuse your sheet and your finished sheet should have a smooth mirror like finish on one side. Wet Layup: While prepreg already has the resin in it, wet layup is when dry carbon or fiberglass has the resin added to it by the user. Generally the cloth is put in place and paint brushes are used to distribute the resin. We have found that wet layup can be easier for complex geometry since it seems to be easier to work into place. While prepreg is generally easier and has better quality if the geometry allows it. The first step to a wet lay up is to wet out the area you plan to layup on. This means covering the surface completely with resin. This resin can by applied with a paint brush. Once the whole surface is covered you can lay a layer of fiber cloth on using best effort to keep the winkles out of the fiber cloth. Then you will use a paint brush to apply resin the the fiber cloth. You can use the brush to pull the remaining wrinkles out of the fiber cloth. Once the fiber cloth is completely wetted out, you can apply a layer of peel ply to the surface. This peel ply will give you a smoother surface. To do this cut the peel ply and set it on top of the wetted out fiber cloth. Then using a pain brush with a small amount of resin on it, you must lightly brush the peel ply so that it is about half "wetted out" and smooth against the fiber cloth. Layup procedures and tips: Tips: * Make sure you use enough resin to wet the carbon fiber. * Make sure the piece of carbon fiber is clean before pouring the resin on it. * Have couple extra inches on the edges of the vacuum bag when covering the carbon fiber to well wet it with resin. * Wear safety glasses during the whole process and change gloves often. Carbon Fiber Infusion (Vacuum Assisted Resin Transfer Molding): This process does not involve wetting out any fibers before the layup. A really good application is for large flat plates where the resin content needs to be minimal to conserve the strength/weight ratio of the panel. The process starts with the layup surface if laying up a flat plate, a large pane of glass is an ideal surface. This is a very flat surface perfect for large panels, and can be cleaned to a beautiful shine. To prepare the layup surface a mold release needs to be applied; at least one layer. A good mold release is 700 NC from "Frekote", this needs to be applied and then let dry for at least 15 min. Once the mold release is applied the fibers can be laid as a dry stack of material. On top of the fibers, a peel ply type of material needs to be put down, a flow medium, and a layer breather cloth. Once all the fibers are placed down, the vacuum bag and lines can be set up. A special type of "curly" vacuum line needs to be used for this process. The curly line is placed inside of the vacuum bag as close to the part as possible and running the full length of one side (shorter side), but below the flow medium! This is critical as the resin will not flow through the part because it will be trapped by the vacuum bag. One corner of the panel needs a vacuum line attached to the curly line and extending about 2 feet out, this will be the resin in line. On the other side of the part, another curly vacuum line needs to be placed, but both ends need to extend outside of the vacuum bag, both ends of this side will go to the vacuum pump. Seal all the edges of the bag with tacky tape, ensuring any necessary pleats are placed correctly. Once the part is fully sealed with the vacuum bag, the resin required needs to be prepared. A good wet layup 2 part resin is "635 Thin Epoxy Resin" from US Composites. This comes with a hardener, and is a 3:1 ratio.The appropriate quantity of resin will depend on the thickness of the fibers and the surface area of the plate. The quantity of resin can be determined through small-scale tests, then upscaled. With the resin mixed the vacuum pump can be turned on. Ensure that the resin in line is kept plugged to allow for full vacuum to be reached. With full vacuum, dip the resin in vacuum line into the resin. (be sure to not pull any air!) The resin will be pulled through the line, through the curly line, and then will spread out across the part. The resin will pull from one side of the part to the other. Once it reaches the other side, the excess will be pulled out through the other curly line. If your vacuum has a resin trap the excess will not damage your pump. Once the part is fully wetted, kink/seal the resin in vacuum line. Allow the part to cure for at least 10 hours with full vacuum pressure. Once cured, follow your required vacuum shut down procedure, and remove the part! If layed up on a glass surface that is clean (aside from the mold release), the surface finish of the face downside will be a gloss! The quality of the surface finish of the topside will depend on the peel ply used. The mold release left over can be reused for another layup if required, it is essentially a wax and doesn't degrade too quickly (unless scratched). Flocked Cotton Epoxy (Flox): Flocked cotton is a structural additive for epoxy resin. This mixture, referred to as flox, can be used to fill gaps and adhere parts to a composite structure. Often, flox is used to reinforce a sharp corner or fill holes left behind from cleco fasteners. Prior to application, all bonding surfaces should be scuffed up to promote adhesion. The proper ratio of flocked cotton to epoxy is a two to one ratio based on volume, but the final consistency should resemble that of creamy peanut butter. It is easiest to mix the epoxy resin at the proper mixture first, then add in the flocked cotton while stirring the mixture. Dry time of this mixture is dependent on the dry time of the epoxy used.